Identifying and disentangling social and physical environmental effects on physical activity in diverse adolescent and young adult populations PROJECT SUMMARY AND ABSTRACT The purpose of this K01 award is to provide developmental support to Dr. Leah Frerichs to become an independent investigator in youth-engaged research using mobile technology and systems science methods to disentangle and address social and physical environment influences on physical activity. Physical activity levels dramatically decrease in adolescence and young adulthood. During these developmental periods, emerging evidence indicates the social and physical environment plays a critical role in shaping physical activity behaviors. However, we have a critical gap in disentangling the effects of different social processes (friendship initiation based on behaviors and similarities versus adoption of friend?s behaviors) and shared exposures to exogenous influences such as activity-promoting built environment features on activity behaviors, especially among African American youth in rural, low-income communities. Teasing apart these intertwined environmental influences requires high-validity, fine-grained, longitudinal data on real- time changes in youth?s social networks, environmental exposures and activity behaviors. With this K01, Dr. Frerichs will build on her experience in community-based research and systems science to obtain formal didactic and hands-on instruction in longitudinal social network and spatial analysis methods, processing and analysis of accelerometry data, mobile technology data collection methods, development of network- and mobile-based intervention strategies, and social and behavioral research ethics and responsible conduct in research. The proposed studies include a secondary analysis of rich data collected using sensors embedded in smartphones that provided real-time objective data on social interactions, geo-coded location data, and physical activity levels among college students. Dr. Frerichs will use the findings and experience from the secondary analysis to inform a primary data collection study with adolescent youth in a rural, African American population. With these data and advanced network modeling techniques, we will examine unanswered questions about networks, environments, and behavior. How much does your peers? activity influence your own activity? Or do your activity behaviors determine who your peers are? And do the spaces where you interact with your peers influence your activity levels? Furthermore, we will examine these questions across critical adolescence to young adult populations, including within a rural African American community where we have critical research gaps. Finally, Dr. Frerichs will use innovative youth-engaged and participatory systems science methods to translate the findings into new social and physical environment intervention strategies. The proposed training and expert mentoring team will provide Dr. Frerichs with the set of skills and preliminary data needed to successfully compete for R01 funding and to serve as a leader in the field of youth-engaged intervention research that uses mobile technology to address social and physical environment influences on obesity-related lifestyle behaviors in underserved communities.